In the manufacture of glass containers, various types of defects may occur. It has heretofore been proposed to utilize optical scanning techniques for inspecting such containers for defects which affect optical transmission characteristics of the container sidewall. In U.S. Pat. Nos. 4,378,493, 4,378,494 and 4,378,495, all of which are assigned to the assignee of the present application, there is disclosed a method and apparatus in which glass containers are conveyed through a plurality of positions or stations where they are physically and optically inspected. At one optical inspection station, a glass container is held in vertical orientation and rotated about its vertical central axis. A light source directs wide angle diffused light energy through the container sidewall. A camera, which includes a plurality of light sensitive elements, i.e., pixels, oriented in a linear array parallel to the vertical axis of container roation, is positioned to view light transmitted through a vertical strip of the container sidewall. The output of each light sensitive element is sampled at increments of container rotation, and event signals are generated when the magnitude of adjacent pixel signals differs by more than a preselected threshold level. An appropriate reject signal is thus produced and the defective container is sorted from the conveyor line.
The method and apparatus disclosed in the aforementioned patents, commonly referred to as the Sidewall Inspection Device (SID), have been found to be very effective and efficient for automated inspection and sorting of glass containers. The present SID employs a wide source of light energy. The source is wide enough so that most refractive defects do not refract the light enough to be visible as a dark spot on the bright background of the wide source. However, because opaque defects absorb or block transmission of light energy, they are visible as dark spots on a bright background. In other words, the present SID detects opaque defects, but is blind to many refractive defects. An "event" signal will be associated with the dark spot when the magnitudes of adjacent pixel signals differ by more than a predetermined threshold. The event occurs at a specific "location" on the sidewall of a container. The event location is defined by the angular position of the container and the pixel number on the linear array which corresponds to the longitudinal position of the defect along container sidewall. The present SID also performs a connectivity analysis by evaluating the locations of a plurality of events to determine whether an opaque defect is present. For example, a tight grouping of events would indicate the presence of an opaque defect, whereas a loose grouping of events would not.